1. Field of the Invention
The present invention relates to a standard light source used for measuring optical characteristics such as total luminous flux of a light source and a measurement method with the use of the standard light source.
2. Description of the Background Art
Total luminous flux (lumen: lm) has conventionally been evaluated as one of optical characteristics of light sources and luminaires. For general measurement of total luminous flux, a standard light source of which value for total luminous flux has already been known (that is, calibrated in advance) is employed. More specifically, by comparing total luminous flux (or illuminance) measured in a state that a standard light source is turned on with total luminous flux (or illuminance) measured in a state that a light source which is a measurement target is turned on in the same measurement system (typically, an integrating sphere), a value for total luminous flux of the light source which is the measurement target is calculated.
New light emitting devices such as LEDs (Light Emitting Diodes) and organic EL (Electro Luminescence) have recently widely been used. Such a light emitting device is different in luminous intensity distribution characteristics from conventional fluorescent lamps, incandescent lamps, and the like. With such a difference in luminous intensity distribution characteristics, a new standard light source suitable for measurement of total luminous flux, such as an LED or organic EL, has been proposed (for example, Suguru Irie et al., “New 2π Geometry Total Luminous Flux Standard Lamp,” 11-6, Papers Presented at 2011 (44th) Annual Conference of the Illuminating Engineering Institute of Japan (IEIJ), September 2011, and Kenji Godo et al., “Development of Standard LED for Total Luminous Flux of High-Power LED,” 11-9, Papers Presented at 2011 (44th) Annual Conference of IEIJ, September 2011).
The standard light sources proposed in the documents described above are premised on dedicated design in accordance with luminous intensity distribution characteristics of an LED. Such a standard light source has a more complicated structure, unlike a conventional bulb-type standard light source. In addition, since the standard light sources disclosed in the documents described above include a light source portion and an integrating sphere, a non-light-emitting structure is relatively large in the standard light source.